An engine approaches a vertical cliff with constant speed $$72\,\text{km h}^{-1}$$. When the engine is at a distance of $$0.7\,\text{km}$$ from the cliff, it blows a whistle. The driver hears the echo after a time. The speed of sound in air is $$330\,\text{m s}^{-1}$$.
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A

$$3.88\,\text{s}$$

B

$$4.00\,\text{s}$$

C

$$4.12\,\text{s}$$

D

$$4.24\,\text{s}$$